1. Field of the Invention
This invention relates to a liquid jet recording head which injects liquid and forms flying liquid droplets, thereby accomplishing recording.
2. Description of the Prior Art
Ink jet recording methods (liquid jet recording methods) have recently drawn attention in that noise occurring during recording is negligible, high-speed recording is possible and recording can be accomplished without requiring the special process of fixing images on so-called plain paper.
Among such liquid jet recording methods are those disclosed, for example, in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Patent Application (DOLS) No. 2843064, which have characteristics different from those of other liquid jet recording methods in that heat energy is caused to act on liquid to thereby obtain a driving force for liquid droplet discharge.
That is, the recording methods disclosed in the above-mentioned publications are characterized in that the liquid subjected to the action of the heat energy undergoes a state change which may result in a sharp increase in volume and by the action force resulting from this state change, liquid is discharged from an orifice at the end of the recording head portion, whereby flying liquid droplets are formed and these liquid droplets adhere to the recording medium and recording is accomplished.
The liquid jet recording method disclosed in DOLS No. 2843064 is not only very effectively applicable to the so-called drop-on demand recording method, but also readily permits the recording head portion to be of the full line type and have closely spaced, multiple orifices and therefore provides images of a high degree of resolution and high quality at a high speed.
The recording head portion of the apparatus applied to the above-described recording method is provided with a liquid discharging portion having an orifice provided to discharge and a liguid flow path communicating with the orifice and having as a part of the construction thereof a heat-acting portion in which heat energy for discharging liquid droplets acts on the liquid, and an electro-thermal converting element as means for generating heat energy.
This electro-thermal converting element is provided with a pair of electrodes and a heat-generating resistive layer connected to these electrodes and having a heat-generating area (a heat-generating portion) between these electrodes, and generally has in the upper portion thereof a protection layer covering the electrodes and the surface of the heat-generating portion and is formed on an insulative base plate. Schematic views for illustrating a typical example of the prior art are shown in FIGS. 1(a) and 1(b) of the accompanying drawings. FIG. 1(a) is a fragmentary plan view of the electro-thermal converting element as seen from above, except for the protection layer covering the surface thereof, and FIG. 1(b) is a cross-sectional view of the electro-thermal converting element taken along dot-and-dash line AA' of FIG. 1(a).
As shown in FIG. 1(b), the electrothermal converting element is of a structure in which a heat-generating resistive material layer 1, an electrode conductor layer 2 and a protection layer 3 are layered on an insulating base plate 4 in the named order from the base plate side, and of these layers, the heat-generating resistive material layer 1 and the electrode conductor layer 2 are patterned in predetermined shapes so as to form a heat-generating portion designated by 103 in FIG. 1(a) and electrode wiring portions 101 and 102 for supplying power to cause heat to be generated in the heat-generating portion 103.
In the fragmentary plan view of FIG. 1(a), only one heat-generating portion is shown for explanation, but the actual electro-thermal converting element is generally of a structure in which a plurality of heat-generating portions are arranged at predetermined intervals.
Now, formation of the heat-generating portion 103 and the electrode wiring portions 101 and 102 is generally effected by the following process. The heat-generating resistive material layer 1 is first formed on the surface of the base plate 4 as by deposition or sputtering, and the electrode conductor layer 2 is further formed on the upper surface thereof by a similar method. Then, by the so-called photoetching method, a part of the electrode conductor layer 2 and a part of the heat-generating resistive material layer 1 are successively removed in accordance with a predetermined pattern, whereby electrode wiring portions 101, 102 and heat-generating portion 103 of desired shapes are formed at desired positions.
During photoetching, etching has heretofore been carried out so that the width of the heat-generating resistive material layer 1 which provides the lower portion of the electrode wiring portions 101 and 102 is equal to the width of the electrode wiring portions 101 and 102. That is, to form the shape of the electrode wiring portions 101 and 102 by the photoetching method, a photo-resist pattern is formed into the desired shape of the electrode wiring portions 101 and 102 on the upper surface of the electrode conductor layer 2, whereafter the unnecessary electrode conductor layer 2 on which the resist pattern is not formed is removed by etching, and then the heat-generating resistive material layer 1 is removed by etching, but in this case, when the heat-generating resistive material layer 1 in the lower portion of the electrode wiring portions 101 and 102 is etched, the relatively thick electrode conductor layer 2 is present in the lower portion of the photoresist and therefore, the heat-generating resistive material layer 1 is readily attached from the side thereof by the etching liquid during the etching of the electrode conductor layer 2 and, as shown in FIG. 1(b), the width of the heat-generating resistive material layer 1 in this portion tends to be narrower than the width of the electrode wiring portions 101 and 102 above it. However, if, in the electrode wiring portions 101 and 102, the edge of the heat-generating resistive material layer 1 which is the lower layer lies inside the edge of the electrode conductor layer which is the upper layer, "curling" or "breakage" will be readily created in the edge of the electrode conductor layer 2.
In the manufacture of the electro-thermal converting element, it is generally known to form the protection layer 3 so as to cover the electrode wiring portions 101 and 102 and, in this case, the side edge portion of the electrode conductor layer 2 juts out with respect to the heat-generating resistive material layer 1 which is the lower layer. Therefore, the coating property of the protection layer 3 for the side edge portion is very poor, and sometimes liquid has entered the electrode wiring portions through the protection layer 3 and has been diffused along the edges of the electrode wiring portions 101 and 102 to moisten the electrode conductor layer 2 and even melt it. Particularly, where the edge portion of the electrode conductor layer 2 is curled as previously described, the coating property of the protection layer 3 becomes poorer and this has led to the readiness with which breakage of the electrode wiring occurs.